The waveform generator or function generator is a commonly-used unit of test equipment in an electronics lab. The function generator produces various electrical waveforms that may be adjusted in frequency, amplitude and offset. In such a device the waveforms are generated by analog circuitry. Adjustments of amplitude were performed by front panel controls (potentiometers) that operated directly on the analog waveform signal. The final signal is then amplified and fed to an output connector.
It is now common practice to use various digital methods to generate the waveforms. This facilitates the use of certain devices such as computer control and the generation of arbitrary waveforms. Since the generation of the shape and frequency of the basic waveform is by means of digital circuitry, it is attractive to control the amplitude and offset by digital methods. Then the entire instrument may be controlled by digital commands. The shape and frequency of the waveform are created by a microprocessor or special-purpose digital hardware that generates a stream of numbers. Each number represents a point on the waveform. Then this stream of digital numbers may be converted into a waveform of voltage or current versus time by a digital-analog converter.
In one possible well known implementation, adjustment of the amplitude and offset is performed as digital number manipulations in the microprocessor or digital hardware, preceding the digital-analog conversion. The amplitude adjustment is performed by multiplying the waveform data by a constant value. The offset adjustment is performed by further adding a constant value. However, performing these arithmetic operations at the speed necessary to generate a reasonable frequency waveform requires a powerful microprocessor (DSP, digital signal processor) or special purpose hardware. As well, the digital-analog converter must have high precision since it must accommodate the entire dynamic range of the output, including the waveform and its DC offset.
Accordingly it would be advantageous to provide a device and a means for controlling a digitally generated waveform that is relatively inexpensive to manufacture. Further it would be advantageous to produce such a device that functions at high speed.